This invention relates to a method of producing IC cards having IC modules embedded therein or attached thereto and, more particularly, to an improvement in the way in which IC modules are embedded in the body of a card.
FIGS. 1 and 2 show in plan and in section an IC card having an IC module disposed inside its body. As shown in FIGS. 1 and 2, the IC card 1 comprises a card body 1a and IC module 2 embedded therein. In detail, the IC card has the IC module 2, external connection terminals 2a of the IC module 2, an opaque core sheet (resin sheet) 4 having a recess 40 in which the IC module 2 is embedded, transparent surface protection sheets 3 and 5, and an adhesive 6. FIG. 3 shows in section another example of this structure. In this example, the same reference characters are used to indicate components which are identical.
The IC module 2 is embedded in a conventional IC card of this type in such a manner that the recess 40 into which the IC module 2 is fitted is formed in the card body 1a, and the bottom of the IC module 2 is bonded to the bottom of the recess 40 of the card body 1a by the adhesive sheet 6. The card body 1a has uniform thickness overall.
In detail, the card body 1a to which the IC module 2 is attached, is formed of hard polyvinyl chloride sheets, and a design is printed by silk screen printing or offset printing on the surface of the core sheet 4 formed from an opaque sheet which forms the face of the card. The transparent protection sheets 3 and 5 of relatively smaller thicknesses are laid over two surfaces of the core sheet 4 and are integrally connected thereto by heating and pressing, thereby forming the card. There are two methods of making the card: one in which the recess 40 into which the IC module 2 is fitted is formed in the card body and the IC module 2 is mounted in the recess 40 by the adhesive 6 after the card body has been formed; and another in which the recess 40 is formed in the card body, the IC module 2 is mounted in the recess 40 by the adhesive 6, and these members are integrally combined by heating and pressing, thereby forming the IC card.
In the above-described production method, the IC module is bonded to the card body by an adhesive sheet having the same size as the bottom surface of the IC module. In this case, there is no problem if the volume of the recess formed in the card body is equal to the sum of those of the IC module and the adhesive sheet. However, if the volume or depth of the recess of the card body is greater than the corresponding parameters of the module and adhesive sheet, the IC module will not be adequately pressed when it is bonded by heating and pressing. A portion of the card corresponding to the IC module is recessed relative to the surface of the card (refer to FIG. 4A). Even if the card has a flat surface after it is finished, the material of the sheet member of the card body outside the recess partially flows into the recess because of the excessive volume of the recess when it is heated and pressed. Correspondingly, the design printed on the core sheet at the back of the IC module may be displaced locally, resulting in local deformation of the card design. Conversely, if the volume or depth of the recess formed in the card body is smaller than the corresponding parameters of the IC module and the adhesive sheet, then, the IC module will protrude beyond the surface of the card, or the thickness of a card portion at the IC module will be greater than the thickness of other portions, as shown in FIG. 4B. Therefore, this protruding portion is locally pressed at a higher pressure during heating and pressing, the core sheet at the rear of the IC module is locally extruded outward, and the design printed on the core sheet at the back of the IC module is locally deformed, resulting in a poor appearance.